Change player names
Release a player as a free agent. You can now rename him, then resign him.

Change player skills
Go to "Player Management", then to "View Roster". Select the player you want to power up or down. Press R or L until you see his "Pitching" or "Batting" attributes. The red area in all of the bars represents how skilled that player is in the category shown next to it. Press Left or Right to increase or decrease the skill.

if you cannot download trainer then go to Chrome/Firefox's settings, specifically to the Privacy settings and simply unchecking the "Enable phishing and malware protection" option.

Some Game Trainers are sometimes reported to be a Virus or Trojan,
the most common is a keylogger called HotKeysHook or the file
has been packed/protected with VMProtect or Themida and
is recognized as Win32/Packed.VMProtect or Win32/Packed.Themida.
In ALL cases this is a FALSE ALARM as NONE
of the Game Trainers @ GCW contain known malicious code! More info in
the PC
Games FAQ!